1================================== 2GPIO Descriptor Consumer Interface 3================================== 4 5This document describes the consumer interface of the GPIO framework. Note that 6it describes the new descriptor-based interface. For a description of the 7deprecated integer-based GPIO interface please refer to gpio-legacy.txt. 8 9 10Guidelines for GPIOs consumers 11============================== 12 13Drivers that can't work without standard GPIO calls should have Kconfig entries 14that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to 15obtain and use GPIOs are available by including the following file: 16 17 #include <linux/gpio/consumer.h> 18 19There are static inline stubs for all functions in the header file in the case 20where GPIOLIB is disabled. When these stubs are called they will emit 21warnings. These stubs are used for two use cases: 22 23- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that 24 the current platform does not enable or select GPIOLIB because we are not 25 going to execute the system anyway. 26 27- Truly optional GPIOLIB support - where the driver does not really make use 28 of the GPIOs on certain compile-time configurations for certain systems, but 29 will use it under other compile-time configurations. In this case the 30 consumer must make sure not to call into these functions, or the user will 31 be met with console warnings that may be perceived as intimidating. 32 33All the functions that work with the descriptor-based GPIO interface are 34prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy 35interface. No other function in the kernel should use these prefixes. The use 36of the legacy functions is strongly discouraged, new code should use 37<linux/gpio/consumer.h> and descriptors exclusively. 38 39 40Obtaining and Disposing GPIOs 41============================= 42 43With the descriptor-based interface, GPIOs are identified with an opaque, 44non-forgeable handler that must be obtained through a call to one of the 45gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the 46device that will use the GPIO and the function the requested GPIO is supposed to 47fulfill:: 48 49 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id, 50 enum gpiod_flags flags) 51 52If a function is implemented by using several GPIOs together (e.g. a simple LED 53device that displays digits), an additional index argument can be specified:: 54 55 struct gpio_desc *gpiod_get_index(struct device *dev, 56 const char *con_id, unsigned int idx, 57 enum gpiod_flags flags) 58 59For a more detailed description of the con_id parameter in the DeviceTree case 60see Documentation/driver-api/gpio/board.rst 61 62The flags parameter is used to optionally specify a direction and initial value 63for the GPIO. Values can be: 64 65* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set 66 later with one of the dedicated functions. 67* GPIOD_IN to initialize the GPIO as input. 68* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0. 69* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1. 70* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line 71 to be electrically used with open drain. 72* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line 73 to be electrically used with open drain. 74 75The two last flags are used for use cases where open drain is mandatory, such 76as I2C: if the line is not already configured as open drain in the mappings 77(see board.txt), then open drain will be enforced anyway and a warning will be 78printed that the board configuration needs to be updated to match the use case. 79 80Both functions return either a valid GPIO descriptor, or an error code checkable 81with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned 82if and only if no GPIO has been assigned to the device/function/index triplet, 83other error codes are used for cases where a GPIO has been assigned but an error 84occurred while trying to acquire it. This is useful to discriminate between mere 85errors and an absence of GPIO for optional GPIO parameters. For the common 86pattern where a GPIO is optional, the gpiod_get_optional() and 87gpiod_get_index_optional() functions can be used. These functions return NULL 88instead of -ENOENT if no GPIO has been assigned to the requested function:: 89 90 struct gpio_desc *gpiod_get_optional(struct device *dev, 91 const char *con_id, 92 enum gpiod_flags flags) 93 94 struct gpio_desc *gpiod_get_index_optional(struct device *dev, 95 const char *con_id, 96 unsigned int index, 97 enum gpiod_flags flags) 98 99Note that gpio_get*_optional() functions (and their managed variants), unlike 100the rest of gpiolib API, also return NULL when gpiolib support is disabled. 101This is helpful to driver authors, since they do not need to special case 102-ENOSYS return codes. System integrators should however be careful to enable 103gpiolib on systems that need it. 104 105For a function using multiple GPIOs all of those can be obtained with one call:: 106 107 struct gpio_descs *gpiod_get_array(struct device *dev, 108 const char *con_id, 109 enum gpiod_flags flags) 110 111This function returns a struct gpio_descs which contains an array of 112descriptors. It also contains a pointer to a gpiolib private structure which, 113if passed back to get/set array functions, may speed up I/O proocessing:: 114 115 struct gpio_descs { 116 struct gpio_array *info; 117 unsigned int ndescs; 118 struct gpio_desc *desc[]; 119 } 120 121The following function returns NULL instead of -ENOENT if no GPIOs have been 122assigned to the requested function:: 123 124 struct gpio_descs *gpiod_get_array_optional(struct device *dev, 125 const char *con_id, 126 enum gpiod_flags flags) 127 128Device-managed variants of these functions are also defined:: 129 130 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, 131 enum gpiod_flags flags) 132 133 struct gpio_desc *devm_gpiod_get_index(struct device *dev, 134 const char *con_id, 135 unsigned int idx, 136 enum gpiod_flags flags) 137 138 struct gpio_desc *devm_gpiod_get_optional(struct device *dev, 139 const char *con_id, 140 enum gpiod_flags flags) 141 142 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, 143 const char *con_id, 144 unsigned int index, 145 enum gpiod_flags flags) 146 147 struct gpio_descs *devm_gpiod_get_array(struct device *dev, 148 const char *con_id, 149 enum gpiod_flags flags) 150 151 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev, 152 const char *con_id, 153 enum gpiod_flags flags) 154 155A GPIO descriptor can be disposed of using the gpiod_put() function:: 156 157 void gpiod_put(struct gpio_desc *desc) 158 159For an array of GPIOs this function can be used:: 160 161 void gpiod_put_array(struct gpio_descs *descs) 162 163It is strictly forbidden to use a descriptor after calling these functions. 164It is also not allowed to individually release descriptors (using gpiod_put()) 165from an array acquired with gpiod_get_array(). 166 167The device-managed variants are, unsurprisingly:: 168 169 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) 170 171 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) 172 173 174Using GPIOs 175=========== 176 177Setting Direction 178----------------- 179The first thing a driver must do with a GPIO is setting its direction. If no 180direction-setting flags have been given to gpiod_get*(), this is done by 181invoking one of the gpiod_direction_*() functions:: 182 183 int gpiod_direction_input(struct gpio_desc *desc) 184 int gpiod_direction_output(struct gpio_desc *desc, int value) 185 186The return value is zero for success, else a negative errno. It should be 187checked, since the get/set calls don't return errors and since misconfiguration 188is possible. You should normally issue these calls from a task context. However, 189for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part 190of early board setup. 191 192For output GPIOs, the value provided becomes the initial output value. This 193helps avoid signal glitching during system startup. 194 195A driver can also query the current direction of a GPIO:: 196 197 int gpiod_get_direction(const struct gpio_desc *desc) 198 199This function returns 0 for output, 1 for input, or an error code in case of error. 200 201Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO 202without setting its direction first is illegal and will result in undefined 203behavior!** 204 205 206Spinlock-Safe GPIO Access 207------------------------- 208Most GPIO controllers can be accessed with memory read/write instructions. Those 209don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ 210handlers and similar contexts. 211 212Use the following calls to access GPIOs from an atomic context:: 213 214 int gpiod_get_value(const struct gpio_desc *desc); 215 void gpiod_set_value(struct gpio_desc *desc, int value); 216 217The values are boolean, zero for low, nonzero for high. When reading the value 218of an output pin, the value returned should be what's seen on the pin. That 219won't always match the specified output value, because of issues including 220open-drain signaling and output latencies. 221 222The get/set calls do not return errors because "invalid GPIO" should have been 223reported earlier from gpiod_direction_*(). However, note that not all platforms 224can read the value of output pins; those that can't should always return zero. 225Also, using these calls for GPIOs that can't safely be accessed without sleeping 226(see below) is an error. 227 228 229GPIO Access That May Sleep 230-------------------------- 231Some GPIO controllers must be accessed using message based buses like I2C or 232SPI. Commands to read or write those GPIO values require waiting to get to the 233head of a queue to transmit a command and get its response. This requires 234sleeping, which can't be done from inside IRQ handlers. 235 236Platforms that support this type of GPIO distinguish them from other GPIOs by 237returning nonzero from this call:: 238 239 int gpiod_cansleep(const struct gpio_desc *desc) 240 241To access such GPIOs, a different set of accessors is defined:: 242 243 int gpiod_get_value_cansleep(const struct gpio_desc *desc) 244 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value) 245 246Accessing such GPIOs requires a context which may sleep, for example a threaded 247IRQ handler, and those accessors must be used instead of spinlock-safe 248accessors without the cansleep() name suffix. 249 250Other than the fact that these accessors might sleep, and will work on GPIOs 251that can't be accessed from hardIRQ handlers, these calls act the same as the 252spinlock-safe calls. 253 254 255The active low and open drain semantics 256--------------------------------------- 257As a consumer should not have to care about the physical line level, all of the 258gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with 259the *logical* value. With this they take the active low property into account. 260This means that they check whether the GPIO is configured to be active low, 261and if so, they manipulate the passed value before the physical line level is 262driven. 263 264The same is applicable for open drain or open source output lines: those do not 265actively drive their output high (open drain) or low (open source), they just 266switch their output to a high impedance value. The consumer should not need to 267care. (For details read about open drain in driver.txt.) 268 269With this, all the gpiod_set_(array)_value_xxx() functions interpret the 270parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line 271level will be driven accordingly. 272 273As an example, if the active low property for a dedicated GPIO is set, and the 274gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level 275will be driven low. 276 277To summarize:: 278 279 Function (example) line property physical line 280 gpiod_set_raw_value(desc, 0); don't care low 281 gpiod_set_raw_value(desc, 1); don't care high 282 gpiod_set_value(desc, 0); default (active high) low 283 gpiod_set_value(desc, 1); default (active high) high 284 gpiod_set_value(desc, 0); active low high 285 gpiod_set_value(desc, 1); active low low 286 gpiod_set_value(desc, 0); default (active high) low 287 gpiod_set_value(desc, 1); default (active high) high 288 gpiod_set_value(desc, 0); open drain low 289 gpiod_set_value(desc, 1); open drain high impedance 290 gpiod_set_value(desc, 0); open source high impedance 291 gpiod_set_value(desc, 1); open source high 292 293It is possible to override these semantics using the set_raw/get_raw functions 294but it should be avoided as much as possible, especially by system-agnostic drivers 295which should not need to care about the actual physical line level and worry about 296the logical value instead. 297 298 299Accessing raw GPIO values 300------------------------- 301Consumers exist that need to manage the logical state of a GPIO line, i.e. the value 302their device will actually receive, no matter what lies between it and the GPIO 303line. 304 305The following set of calls ignore the active-low or open drain property of a GPIO and 306work on the raw line value:: 307 308 int gpiod_get_raw_value(const struct gpio_desc *desc) 309 void gpiod_set_raw_value(struct gpio_desc *desc, int value) 310 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc) 311 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) 312 int gpiod_direction_output_raw(struct gpio_desc *desc, int value) 313 314The active low state of a GPIO can also be queried using the following call:: 315 316 int gpiod_is_active_low(const struct gpio_desc *desc) 317 318Note that these functions should only be used with great moderation; a driver 319should not have to care about the physical line level or open drain semantics. 320 321 322Access multiple GPIOs with a single function call 323------------------------------------------------- 324The following functions get or set the values of an array of GPIOs:: 325 326 int gpiod_get_array_value(unsigned int array_size, 327 struct gpio_desc **desc_array, 328 struct gpio_array *array_info, 329 unsigned long *value_bitmap); 330 int gpiod_get_raw_array_value(unsigned int array_size, 331 struct gpio_desc **desc_array, 332 struct gpio_array *array_info, 333 unsigned long *value_bitmap); 334 int gpiod_get_array_value_cansleep(unsigned int array_size, 335 struct gpio_desc **desc_array, 336 struct gpio_array *array_info, 337 unsigned long *value_bitmap); 338 int gpiod_get_raw_array_value_cansleep(unsigned int array_size, 339 struct gpio_desc **desc_array, 340 struct gpio_array *array_info, 341 unsigned long *value_bitmap); 342 343 int gpiod_set_array_value(unsigned int array_size, 344 struct gpio_desc **desc_array, 345 struct gpio_array *array_info, 346 unsigned long *value_bitmap) 347 int gpiod_set_raw_array_value(unsigned int array_size, 348 struct gpio_desc **desc_array, 349 struct gpio_array *array_info, 350 unsigned long *value_bitmap) 351 int gpiod_set_array_value_cansleep(unsigned int array_size, 352 struct gpio_desc **desc_array, 353 struct gpio_array *array_info, 354 unsigned long *value_bitmap) 355 int gpiod_set_raw_array_value_cansleep(unsigned int array_size, 356 struct gpio_desc **desc_array, 357 struct gpio_array *array_info, 358 unsigned long *value_bitmap) 359 360The array can be an arbitrary set of GPIOs. The functions will try to access 361GPIOs belonging to the same bank or chip simultaneously if supported by the 362corresponding chip driver. In that case a significantly improved performance 363can be expected. If simultaneous access is not possible the GPIOs will be 364accessed sequentially. 365 366The functions take three arguments: 367 * array_size - the number of array elements 368 * desc_array - an array of GPIO descriptors 369 * array_info - optional information obtained from gpiod_array_get() 370 * value_bitmap - a bitmap to store the GPIOs' values (get) or 371 a bitmap of values to assign to the GPIOs (set) 372 373The descriptor array can be obtained using the gpiod_get_array() function 374or one of its variants. If the group of descriptors returned by that function 375matches the desired group of GPIOs, those GPIOs can be accessed by simply using 376the struct gpio_descs returned by gpiod_get_array():: 377 378 struct gpio_descs *my_gpio_descs = gpiod_get_array(...); 379 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, 380 my_gpio_descs->info, my_gpio_value_bitmap); 381 382It is also possible to access a completely arbitrary array of descriptors. The 383descriptors may be obtained using any combination of gpiod_get() and 384gpiod_get_array(). Afterwards the array of descriptors has to be setup 385manually before it can be passed to one of the above functions. In that case, 386array_info should be set to NULL. 387 388Note that for optimal performance GPIOs belonging to the same chip should be 389contiguous within the array of descriptors. 390 391Still better performance may be achieved if array indexes of the descriptors 392match hardware pin numbers of a single chip. If an array passed to a get/set 393array function matches the one obtained from gpiod_get_array() and array_info 394associated with the array is also passed, the function may take a fast bitmap 395processing path, passing the value_bitmap argument directly to the respective 396.get/set_multiple() callback of the chip. That allows for utilization of GPIO 397banks as data I/O ports without much loss of performance. 398 399The return value of gpiod_get_array_value() and its variants is 0 on success 400or negative on error. Note the difference to gpiod_get_value(), which returns 4010 or 1 on success to convey the GPIO value. With the array functions, the GPIO 402values are stored in value_array rather than passed back as return value. 403 404 405GPIOs mapped to IRQs 406-------------------- 407GPIO lines can quite often be used as IRQs. You can get the IRQ number 408corresponding to a given GPIO using the following call:: 409 410 int gpiod_to_irq(const struct gpio_desc *desc) 411 412It will return an IRQ number, or a negative errno code if the mapping can't be 413done (most likely because that particular GPIO cannot be used as IRQ). It is an 414unchecked error to use a GPIO that wasn't set up as an input using 415gpiod_direction_input(), or to use an IRQ number that didn't originally come 416from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. 417 418Non-error values returned from gpiod_to_irq() can be passed to request_irq() or 419free_irq(). They will often be stored into IRQ resources for platform devices, 420by the board-specific initialization code. Note that IRQ trigger options are 421part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup 422capabilities. 423 424 425GPIOs and ACPI 426============== 427 428On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by 429the _CRS configuration objects of devices. Those resources do not provide 430connection IDs (names) for GPIOs, so it is necessary to use an additional 431mechanism for this purpose. 432 433Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object 434which, among other things, may be used to provide connection IDs for specific 435GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the 436case, it will be handled by the GPIO subsystem automatically. However, if the 437_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO 438connection IDs need to be provided by device drivers. 439 440For details refer to Documentation/acpi/gpio-properties.txt 441 442 443Interacting With the Legacy GPIO Subsystem 444========================================== 445Many kernel subsystems still handle GPIOs using the legacy integer-based 446interface. Although it is strongly encouraged to upgrade them to the safer 447descriptor-based API, the following two functions allow you to convert a GPIO 448descriptor into the GPIO integer namespace and vice-versa:: 449 450 int desc_to_gpio(const struct gpio_desc *desc) 451 struct gpio_desc *gpio_to_desc(unsigned gpio) 452 453The GPIO number returned by desc_to_gpio() can be safely used as long as the 454GPIO descriptor has not been freed. All the same, a GPIO number passed to 455gpio_to_desc() must have been properly acquired, and usage of the returned GPIO 456descriptor is only possible after the GPIO number has been released. 457 458Freeing a GPIO obtained by one API with the other API is forbidden and an 459unchecked error. 460